A cellular immune system is one of immune protective mechanisms against invading antigens.
Many means for enhancing cellular immune responses have been known. One example is the administration of agents of stimulating immune cells such as cytokine and the like. Vaccines inducing immune responses specific for infecting antigens also enhance the cellular immune system. Further, Some adjuvants used in combination with vaccines such as LPS enhances non-specific immune responses.
It has been well documented that many agents with strong stimulatory effects on macrophages either contain carbohydrate (e.g. zymosan, LPS) or are chemically similar to carbohydrate (e.g. pyran) (1, 2). Several β-glucans have been shown to stimulate various facets of cellular immune responses. For example, in vitro studies have revealed that β-glucans activate macrophages, neutorphils, and NK cells to kill sensitive tumor cells (2–6) as well as potentiate T cell responses to cellular antigens (7). High molecular weight β-glucans have been shown to stimulate neutrophil degranulation and respiratory bursts (8) and secretion of IL-1, TNF-α, GM-CSF, and IL-6 from macrophages (9, 10). Numerous studies have demonstrated that β-glucans, either soluble or particulate, isolated from various natural sources and wide variable molecular sizes and secondary structures, exhibit antitumor and antimicrobial activities in mouse model system(3, 4, 6, 11). Some of them have been applied clinically for tumor immunotherapy, such as the fungal β-glucan, lentinan and schzophillan (13–16).
The fact that β-glucans which have no significant side-effect and are safe in pharmaceutical use act to enhance a cellular immunity should be noticed in order to treat many types of infection and tumor more effectively. So, there is still necessity to study β-glucans directed to the immune system, especially the enhancement of a cellular immunity.